hostname: detect detachable dmi chassis type (#5489)

Detect the 'Detachable' dmi chassis type properly. Use the new
'convertible' chassis class of hostnamed, instead of returning the
generic 'computer' chassis class.

src/hostname/hostnamed.c

@@ -202,6 +202,7 @@ static const char* fallback_chassis(void) {
                 return "tablet";
 
         case 0x1F: /* Convertible */
+        case 0x20: /* Detachable */
                 return "convertible";
         }